chore: remove unused backend dependencies

[telemarkdigital-publisher]

Summary

• remove unused direct dependencies: @noble/ed25519, @opentelemetry/sdk-trace-node, cors, and dotenv
• remove unused direct devDependency @opentelemetry/core while keeping transitive OpenTelemetry lock entries required by SDK packages
• update npm and pnpm lockfiles plus README dependency notes

Closes #220.

Validation

• git diff --check
• package.json/package-lock.json JSON parse check
• code search found no source/test imports for the removed direct dependencies

Local limitation

• npm run build could not complete in this local workspace because the current node_modules install is incomplete/missing declared packages and npm install is blocked by the pre-existing redis@^4.9.0 resolution error.